Charge ordering phenomena in high temperature superconductors

The electronic Raman effect has been studied in single crystals of Y1-xCaxBa2Cu3O6 (Y-123) and La2-xSrxCuO4 (LSCO) at different doping. The experimental results provide evidences of an anomalous contribution to the response at low energies and temperatures. In LSCO the additional excitation is in B2g symmetry for x = 0.02 and in B1g symmetry for x = 0.10. In Y-123, we observed the additional feature in B2g symmetry at 1.5% doping. Mainly on the basis of the selection rules we conclude that the additional peaks are the response of a dynamical charge modulation (stripes) in the two-dimensional CuO2 planes. The selection rules allow us to determine the orientation of the stripes to be along the diagonal of the CuO2 planes in Y-123 and LSCO at x = 0.02, and along the principal axes in LSCO at x = 0.10